Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several small-sized cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery pack having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the medium- or large-sized devices.
Unit cells used for medium- or large-sized battery packs are classified approximately into a cylindrical battery, a rectangular battery, and a pouch-shaped battery. For early medium- or large-sized battery packs, the cylindrical battery was used as a unit cell. For example, Japanese Unexamined Patent Publication No. 2004-247320 discloses a method of manufacturing a battery pack by connecting cylindrical batteries with each other in the horizontal direction, while the cylindrical batteries are mounted to a fixing plate having a specific shape, and connecting the cylindrical batteries with each other in the vertical direction using connection rings and insulation rings. However, the above-mentioned publication has problems in that the connection between the plurality of cylindrical batteries so as to manufacture the battery pack requires a large number of connecting members due to the structural characteristics of the cylindrical batteries, and therefore, the assembly process of the battery pack is complicated, which greatly increases the manufacturing costs of the battery pack. Furthermore, there exist a large number of dead spaces between the cylindrical batteries. For this reason, the cylindrical batteries have fundamental limits in consideration of the recent demand of battery packs having a compact structure.
Consequently, there has been carried out much research on plate-shaped batteries, such as a rectangular battery and a pouch-shaped battery, which can be easily assembled with a reduced number of connecting members and can be stacked with high density. Especially, a high interest is taken in the pouch-shaped battery, which is lightweight and can be manufactured with low manufacturing costs.
The plate-shaped battery has an advantage in that the battery pack can be easily manufactured using a few number of connecting members, while the size of the dead space is greatly reduced, due to the structural characteristics of the plate-shaped battery. However, the plate-shaped battery, especially, the pouch-shaped battery, has low mechanical strength. For these reasons, for example, one to five batteries are mounted in a case having adequate mechanical strength, or the batteries are connected by additional members, so as to constitute a battery module, and a plurality of battery modules are stacked one on another based on desired capacity and output, so as to manufacture a battery pack.
Typical examples of such battery packs are disclosed in Korean Unexamined Patent Publication No. 2005-0036751, which has been filed in the name of the applicant of the present patent application, Japanese Unexamined Patent Publication No. 2004-31049, Japanese Unexamined Patent Publication No. 2004-247320, and U.S. Unexamined Patent Publication No. 2003-170535. These publications have their own advantages in constructing the battery packs using the plate-shaped batteries as unit cells. According to the disclosures of the publications, the plate-shaped unit cells are mechanically and electrically connected with each other, while the unit cells are arranged in the vertical or horizontal direction, so as to constitute a battery module, and a plurality of battery modules are also arranged in the horizontal or vertical direction so as to constitute a medium- or large-sized battery pack.
However, when the plate-shaped batteries are arranged only in the horizontal direction, i.e., in the lateral direction of the plate-shaped batteries, so as to constitute the battery module, the battery module is formed in a thin plate-shaped structure. As a result, the mechanical strength of the battery module is low, and a large number of members (for example, bus bars) are necessary for the electrical connection between electrode terminals of the plate-shaped batteries. On the other hand, when the plate-shaped batteries are arranged only in the vertical direction, i.e., in the thickness direction of the plate-shaped batteries, the horizontal-direction mechanical coupling between battery modules is additionally required to constitute the battery pack. As a result, the assembly process of the battery pack is complicated.
Consequently, the necessity of a battery module, which can be easily manufactured, has sufficient mechanical strength, and allows more efficient manufacture of a battery pack, is highly requested.